1. Field of the Invention
The present invention relates generally to tools for inserting pitot tubes and similar sensing elements into fluid conveying pipelines and removing sensing elements from the fluid conveying pipelines. More particularly, the present invention relates to tools for inserting and removing the sensing elements through stuffing boxes of hot taps in high pressure pipelines without interrupting the flow of fluid in pipelines.
2. Description of the Prior Art
In a fluid conveying pipeline, such as a gas pipeline, water pipeline, or petrochemical pipeline, it is often desirable to collect information about the flow, pressure or other parameters of the fluid flowing in the pipeline by insertion of a measuring device such as a pitot tube, hereinafter sometimes referred to generally as a sensing element, into the flowing fluid. For example, in order to measure flow, an elongated flow sensing element, such as the pitot tube described in U.S. Pat. No. 5,036,711, may be inserted into the flow.
It is also desirable to insert and remove sensing elements while the fluid is present and flowing in the pipeline. This facilitates moving sensing elements from location to location, when it is desired to measure the characteristic of the fluid only periodically, and facilitates removal of the sensing element for maintenance and cleaning and subsequent re-insertion.
In order to accomplish insertion and removal without interrupting flow, hot taps are widely used. A hot tap generally comprises an outlet through a wall of the pipeline conveying the fluid for which a parameter is to be measured. An access valve is connected to the outlet. The access valve is a valve of a type which provides an unobstructed access passageway to the interior of the pipeline when the valve is open. The access valve is connected by an access tube to a packing gland designed to seal around the sensing element while permitting the sensing element to be inserted and removed. To insert the sensing element into the hot tap the access valve is initially closed. An end of the sensing element is first inserted through the packing gland, forming a relatively fluid tight seal between the packing gland and the sensing element. The end of the sensing element is then inserted along a passageway the access tube until the end of the sensing element is near the location of the closed access valve. The access valve is opened, allowing the fluid in the pipeline to enter the access tube. The end of the sensing element is then passed through the access passageway of the access valve until it is inserted a preselected distance into the pipeline. The packing gland is adjusted to tighten the seal and the sensing element is secured by a conventional threaded connector or clamping means to prevent its being pushed out of the pipeline and access tube by fluid pressure. In order to remove the sensing element these steps are reversed.
Many problems are inherent in inserting and removing a sensing element through a hot tap. The pressure of the pipeline may be extremely high, creating a substantial force resisting insertion of the sensing element. In addition, the sensing element is typically long and slender, making it difficult to handle, and creating the possibility of binding at the packing gland and damaging the sensing element if it is not inserted or removed substantially along a longitudinal axis of the passageway of the access tube. In order to insert and remove the sensing element it is necessary to substantially align the sensing element with the longitudinal axis of the access tube before inserting the end of the sensing element into the packing gland. This requires an unobstructed insertion space between the packing gland and the nearest obstruction, such as another pipe, a wall or a ceiling, the insertion space being at least as long as the sensing element. Insertion and removal tools which align with the axis of the sensing element increase the required insertion space, making them difficult to use in restricted spaces. Further complicating matters hot taps are often located in dirt or debris laden environments, in which exposed moving parts of an insertion and removal tool may malfunction due to a buildup of dirt and debris on the moving parts.
Several insertion and removal tools, have been used to partially overcome these problems. Piston driven hydraulic tools have been used to apply an insertion force through a drive rod to the top of the measuring element, pushing the measuring element into the pipeline. These tools can provide the necessary force but are mechanically complex, making them prone to failure. Further, they must be aligned with the longitudinal axis of the sensing element and therefore add substantially to the required insertion space and to the difficulty of handling the sensing element.
Direct insertion tools using threaded stem and nut constructions, with a threaded stems aligned with the longitudinal axis of the sensing element and secured to the top of the sensing element, provide a mechanical advantage for manual insertion and are mechanically simpler than the hydraulic insertion devices, but share the disadvantage of requiring additional unobstructed insertion space. In addition, the threaded stem is directly exposed to the dirt and debris laden environment in which the devices are used, and is thus prone to fouling from dirt and debris. This buildup of dirt and debris on the stem may interfere with proper operation. This problem is accentuated by the fact that such stem and nut arrangements are frequently coated with an oil or grease which tends to retain the dirt and debris on the surface of the threaded stem.
Both the hydraulic piston and the threaded stem and nut tools push the probe into the pipeline against the pipeline pressure. The resulting force on the tool places the drive rod or stem of the tool in compression. When the drive rod or stem is in compression it can bend, possibly damaging the tool and potentially causing the sensing element to not be inserted substantially along the longitudinal axis of the access tube.
A side mounted threaded stem and nut tool which clamps to the access tube of the hot tap and to the top of the sensing element is described in U.S. Pat. No. 4,841,787, to Waterman, issued in 1989. The nut of the Waterman tool is located above a bushing that is slidable along the stem and is connected to the top of the sensing element. An actuating wrench is connected to the nut. When the nut is rotated by the wrench in one direction the nut bears down on the bushing and the sensing element is pushed into the hot tap against the pipeline pressure and friction in the packing gland. When the nut is rotated in the other direction pipeline pressure is allowed to force the sensing element out of the hot tap, controlled by the rotation of the nut. The side mounted stem and nut of the Waterman tool extends only a short distance above the top of the sensing element, thereby reducing the additional insertion space required by some other tools. A certain amount of added insertion space is required, however, to accommodate the actuating wrench, or lever, that is located beyond the end of the sensing element. The threaded stem and nut of the Waterman tool is exposed to the environment and is subject to fouling with dirt and debris. In addition, because the Waterman tool device normally relies on pipeline pressure to provide the force for removing the sensing element from the pipeline, partial disassembly is required to bring a lower nut into contact with the bottom of the slidable bushing in order to remove the sensing element in the event pipeline pressure is inadequate to overcome the frictional forces at the packing gland which may resist removal of a sensing element.
It is against this background that the present invention was developed to provide an improved tool for inserting and removing sensing elements.